What is the closest I can get to a 6mm ortho with decent eye relief?

[Saturninus]

Hello All!

New member here, and I am assembling an eyepiece set for a Celestron Nexstar 8 SE that I recently got for my wife. I've got something in mind for the 20mm and 10mm range, but I'm looking for a high power piece for those rare nights when conditions will let us go above 300X.

I was originally thinking of a Baader Classic Ortho 6mm because I like the idea of an minimalist 4 element design that maximizes contrast (and at a reasonable price!), but realistically that eye relief is going to be too punishing. I know to get better eye relief at 6mm I will have to turn to eyepieces with more complex designs. I could just get a 12mm ortho and add a barlow, but I'm guessing that this is exactly how some of the high-power long eye relief pieces are constructed.

My question is, which of the mid-price level pieces out there is the closest thing to being an ortho with a built-in barlow? I assume such a piece would be a 6 element design. Is something like a Celestron X-cel basically an ortho with a barlow?

My goal is to get 5 or 6mm eyepiece with eye relief of 10mm or greater in the most simple, high contrast-producing design possible. And since this is an eyepiece that I would probably be using less than 10% of the time, I'd rather keep the cost in the mid-range or lower.  (saving the money for the 20mm piece)

Thanks for any suggestions!

[Moonshane]

5mm or 6mm Radian. Used for about £100.

[rwilkey]

Hi Saturninis, the 6mm William Optics SPL is good planetary eyepiece with good eye relief, highly recommended, about $129 I think.

[michael.h.f.wilkinson]

I would not go for a 6mm but for a 7mm at 290x (more like 300x with 2" diagonal). I have tried a 6mm (Nagker 12mm T4 plus Meade TeleXtender 2x) in my GP-C8 (same OTA as yours) and that rarely if ever works. By contrast, some of my best planetary views on nights with super seeing are with 7mm EPs. I used Vixen LV 9 and 7mm for planetary for years (very nice 20mm eye relief, very good quality, decent 45-50 deg FOV). I later replaced these by a 10mm and 8mm TV Radian: very good combination indeed, just a gnats breath ahead of the LVs, but mainly better in terms of FOV. On-axis performance very similar indeed. I never was temptedto get the 6mm Radian for my SCT, but I did miss the 7mm. I finally got the Pentax XF8.5mm and later the XW 7mm and 10mm for planetary, and the latter in particular are superb. I now have a Delos 8mm sitting in between, and the XF mainly in solar work. For planetary the stallwart is the XW 10mm, on good nights the 8mm Delos sees quite a bit of service, and on really good nights the 7mm steals the show.

If you do not want a 70 deg FOV, I would go for a Vixen (N)LV7, or Radian 8mm, if you want the best 7mm for planetary with good eye relief, the XW7 is it. For the C8 OTA, 6mm is over the top.

[Saturninus]

Thanks for all the advice! I assumed the Radians and Pentaxs were out of my reach. But I'll look into the Williams Optical and the Vixens. They sound well suited for my purposes.

I forgot to mention - I plan to use this eyepiece at the visitor center in either Mauna Kea or Haleakala, Hawaii. (I live on a neighboring island). That is at 10,000ft - I hope to have excellent seeing conditions there where I can push the telescope to its limit. Hence the 6mm eyepiece. 

When I am at sea level in ordinary conditions, I'm planning on using an 11m Televue Plossl for planetary observation

[Moonshane]

you'll not make many friends on here telling us that. I am honestly not jealous in any way at all.

[michael.h.f.wilkinson]

I live at sea level (or perhaps just below), and I frequently go beyond 200x. An 11 mm would not be my choice for planetary in the C8. 10 or 9 is better.

[Saturninus]

Well, the other 362 days of the year when I am not observing at the top of Haleakala, I will be sitting in a shoebox of an apartment in an area with so much light pollution I can read a newspaper by the streetlights outside. I would trade places with you if you have a nice backyard where you can see a decent amount of stars on a normal day!

I don't have a good idea how much magnification I can draw out of my telescope under the unique conditions of Mauna Kea or Haleakala, but if I can see really amazing things at 50x per inch of aperture or more, I'd like to take advantage of that!

[itmo]

How about a good barlow and a 12mm ortho? It will have more eyerelief but the same effective focal length. 

[moffer]

I have very limited experience with different eyepieces, so for what it's worth... I really like my William Optics 6mm SPL, it's sharp to edge of field and very comfortable to use in my 200p F6. I bought mine after reading good reviews and favourable reports by owners on this forum.

I have read on the Cloudy Nights forum that the Zhumell Z series planetary eyepieces are the same as the WO SPLs and cheaper to buy - around the $70 mark as I recall. Seems like this is based mainly on conjecture though, as I've yet to come across any reports of direct comparisons between the two makes of eyepiece. The Zhumell also appears to be well regarded for its price.

[michael.h.f.wilkinson]

How about a good barlow and a 12mm ortho? It will have more eyerelief but the same effective focal length.

I hear this suggestion often and I always wonder how that could be better than a planetary long eye relief design. All these designs are is a Smyth lens (= Barlow) in front of a long focal length Plössl or orthoscopic like (or wide angle) group of lenses. The difference is that in the case of the planetary EPs (whether XW, Radian, TMB, LV or otherwise) the Smyth lens is matched to the rest to minimize aberrations while keeping the number of elements/groups down. A top quality Barlow with an orthoscopic EP will do well, but I would not think it would outperform the others.

[itmo]

Well with a televue barlow atleast half of the system is televue  

[michael.h.f.wilkinson]

Well with a televue barlow atleast half of the system is televue

But with a Radian or Delos all of the system is TV

[Mr Spock]

I'd go for a 6mm NLV. An ortho is a little bit brighter, but that's about it. The NLVs are sharp and contrasty.